The present invention relates to a redundant module for decoupling short-circuit currents in a redundant voltage supply.
In electrical systems, machines, or devices which are subject to high requirements in terms of availability and reliability, control and safety related functions are provided by redundant voltage supplies. This redundancy is, for example, ensured by at least two coupled power supply units which feed the respective devices in parallel operation. The output power of the individual power supply units is dimensioned such that at least in case of failure of one of the power supply units, the required electric power is provided by the remaining power supply units.
The parallel-connected, power supply units are routed to a common current node at the output side, from which the total electrical power provided is distributed to respective consumers of a system, machine, or device. In order for the common current node, in the event of a short-circuit at the output side in any of the power supply units which could occur as a result of a defect in the power supply unit, to be not loaded by the resulting short-circuit current, it is necessary for this case to decouple the power supply units from one another. To this end, generally, so called redundant modules are used which provide a separate input for each of the power supply units to be connected in parallel, each of these inputs being routed to a common output, via a decoupling diode. Such a circuit, also known as an O-ring circuit, decouples a short-circuited power supply unit from the common current node at the output of the redundant module, into which node in normal operation all parallel power supply units feed its output current. If, for example, in a short-circuit event the output voltage of a power supply unit drops to zero potential, the result is a negative voltage drop between the corresponding input and the current node at the output of the redundant module, so that the decoupling diode blocks a possible short-circuit current.
In order to have a lowest possible power dissipation at the decoupling diodes in normal operation, a redundant module typically uses Schottky diodes which exhibit a low forward voltage of about 400 mV. Corresponding redundant modules are also known in form of so-called. O-ring diodes as integrated devices.
A disadvantage of the known redundant modules is that the parallel operated redundant power supply units are unevenly loaded when feeding into the common current node, which shortens the operating life of individual power supply units. Another disadvantage of known redundant modules is that the operability of the decoupling diodes and the presence of redundancy cannot be monitored.